In a sentence: The use of repetitive rhythms to induce altered states of consciousness
The usage of repetitive rhythms to induce trance states is nothing new. Shamanistic practioneers have been doing it for thousands of years, the world over. Researchers of this phenomenon have been consistently surprised at the similiarity of shamanistic auditory driving rituals among different cultures, even those separated by vast geographical distances.
Auditory driving works through a process known as entrainment. Basically, entrainment is the sychronization of different rhythmic cycles. Breathing and heart rate have been shown to be affected by auditory stimulus, along with brain wave activity. The ability of rhythmic sound to affect human brain wave activity, especially theta brain waves, is the heart of auditory driving, and is the cause of the altered states of consciousness that it can induce. This increase in theta brain waves induces the state known by Buddhists as walking meditation - it is the state where one can mentally 'disengage' from their current physical activity (in this case, dancing), and the resulting flow of thought is free-flowing, unrestricted, and highly creative.
Auditory driving is not the only way to enter this state - 'classic' meditation will do it, along with long distance running, or even long distance freeway driving (although this can be dangerous), among other techniques. This state of consciousness has been shown to be very psychologically beneficial, by helping to relieve built up stress, allowing one to reflect on life issues without censorship or guilt, and generally giving one a break from consistently operating at alpha or delta states. Generally, one is only in a theta state for a period of minutes, right before going to sleep, and when waking up. Being in a theta state for 15 minutes is considered to be an 'extended period'. With the use of auditory driving, or other meditative techniques, this time can be extended significantly.
The auditory driving phenomenon is still present today, especially among electronic dance music culture, which in many ways is a modern version of shamanism. The same effect is caused by many jam bands, which helps explain people's attraction to them, indeed, their attraction to music in general. Churches which chant their services also have the same effect, causing a meditative state by using odd inflections and off-kilter rhythmic structures.